Global online retail giant Amazon's launch of its Prime Now service has got off to a rocky start with some shoppers unable to place orders on its app.

The service was launched on Thursday but some shoppers were unable to order goods that day.

When this reporter tried to place an order at 11.30am on Friday (July 28) via the Prime Now mobile app, we received a message stating: "No delivery windows are available. All remaining delivery windows for today and tomorrow are currently unavailable. Check again later for updates, or try again tomorrow."

Customers took to Amazon Prime Now's Facebook page to voice their displeasure.

Ms Patricia Yeo wrote at 9.46am on Friday: "Is this really Amazon? Just launched and I couldn't even do a checkout since last night till now because you do not have any delivery windows???"

An Amazon spokesman told TNP on Friday: "We are thrilled customers in Singapore love ultra-fast delivery as much as we do.